Since the discovery of high T.sub.c superconducting materials, many proposals have been made for applications of such materials. The availability of high T.sub.c materials in wire form has led to uses such as transformer windings, (see U.S. Pat. No. 5,107,240 to Tashiro et al); as a superconducting magnet (see U.S. Pat. No. 5,113,165 to Ackermann); for providing superconducting current connectors (see U.S. Pat. No. 4,895,831 to Laskaris); and for other and varied purposes (see U.S. Pat. No. 4,914,081 to Miller et al and U.S. Pat. No. 4,923,850 to Stephan et al.).
In U.S. Pat. No. 5,015,622 to Ward et al., a superconducting stepping motor is described wherein a magnetized article is suspended over a stator and, via appropriate excitation, the magnetized article is moved over the stator's surface. U.S. Pat. No. 5,066,638 to Lloyd et al; and U.S. Pat. No. 5,099,162 to Sawada both describe the use of coils of superconducting material for electric motor winding applications. In each of these patents, support structures for the superconducting windings are conventional bearings.
The use of high T.sub.c superconductors for bearing structures has also been proposed. Such bearings make use of a Meissner-like effect that enables a stable levitating force to be achieved between a source of field lines and a superconducting surface. The Meissner-like effect is the result of a "repulsion" that occurs when field lines are prevented from penetrating a superconducting surface due to circulating currents on the surface that are induced by the field lines. More particularly, when a source of field lines is brought into juxtaposition to a superconducting surface, the field lines are diverted from the superconducting surface and a resulting "magnetic pressure" results between the source of the field lines and the superconducting surface, thereby creating the levitating force.
Bearing structures using Meissner-like effects can be found in U.S. Pat. No. 4,939,120 to Moon et al; U.S. Pat. No. 4,956,571 to Gordon et al and U.S. Pat. No. 5,061,679 to Weeks, II. Each bearing structure shown in the aforesaid patents includes permanent magnets that are positioned in juxtaposition to a superconducting surface. Under such conditions (especially with type II superconductors), when the bearing arrangement is supercooled, certain of the field lines are trapped in the superconducting material and create a "pinning" action. With type I superconductors, a similar flux penetration is seen--but without the pinning effect. In either case, the resulting "pressure" (or levitating force) decreases as the result of the flux penetration. Thus, while levitation pressures can be achieved using such structures, the load-bearing properties of such superconducting bearings is less than optimal.
Accordingly, it is an object of this invention to provide an improved magnetic bearing structure.
It is yet another object of this invention to provide a superconducting bearing structure wherein flux exclusion effects are enhanced.
It is still another object of this invention to provide a method for energizing a superconducting bearing structure wherein penetration of flux into a superconducting surface are minimized.
Another object of this invention is to provide a means to create a higher magnetic field intensity in a superconducting bearing structure than that achieved with permanent magnets.